immutable-js
diff --git a/‎__tests__/merge.ts
Lines changed: 6 additions & 0 deletions b/‎__tests__/merge.ts
Lines changed: 6 additions & 0 deletions
diff --git a/‎src/functional/merge.js
Lines changed: 4 additions & 2 deletions b/‎src/functional/merge.js
Lines changed: 4 additions & 2 deletions
diff --git a/‎src/methods/merge.js
Lines changed: 3 additions & 0 deletions b/‎src/methods/merge.js
Lines changed: 3 additions & 0 deletions
@@ -40,6 +40,12 @@ describe('merge', () => {
     );
   });
 
+  it('throws typeError without merge function', () => {
+    const m1 = Map({ a: 1, b: 2, c: 3 });
+    const m2 = Map({ d: 10, b: 20, e: 30 });
+    expect(() => m1.mergeWith(1, m2)).toThrowError(TypeError);
+  });
+
   it('provides key as the third argument of merge function', () => {
     const m1 = Map({ id: 'temp', b: 2, c: 3 });
     const m2 = Map({ id: 10, b: 20, e: 30 });
 
@@ -38,9 +38,11 @@ export function mergeWithSources(collection, sources, merger) {
     );
   }
   if (isImmutable(collection)) {
-    return collection.mergeWith
+    return typeof merger === 'function' && collection.mergeWith
       ? collect
8000
ion.mergeWith(merger, ...sources)
-      : collection.concat(...sources);
+      : collection.merge
+        ? collection.merge(...sources)
+        : collection.concat(...sources);
   }
   const isArray = Array.isArray(collection);
   let merged = collection;
 
@@ -14,6 +14,9 @@ export function merge(...iters) {
 }
 
 export function mergeWith(merger, ...iters) {
+  if (typeof merger !== 'function') {
+    throw new TypeError('Invalid merger function: ' + merger);
+  }
   return mergeIntoKeyedWith(this, iters, merger);
 }
Original file line number	Diff line number	Diff line change
`@@ -38,9 +38,11 @@ export function mergeWithSources(collection, sources, merger) {`
`38`	`38`	`);`
`39`	`39`	`}`
`40`	`40`	`if (isImmutable(collection)) {`
`41`		`- return collection.mergeWith`
	`41`	`+ return typeof merger === 'function' && collection.mergeWith`
`42`	`42`	`? collect 8000 ion.mergeWith(merger, ...sources)`
`43`		`- : collection.concat(...sources);`
	`43`	`+ : collection.merge`
	`44`	`+ ? collection.merge(...sources)`
	`45`	`+ : collection.concat(...sources);`
`44`	`46`	`}`
`45`	`47`	`const isArray = Array.isArray(collection);`
`46`	`48`	`let merged = collection;`
Original file line number	Diff line number	Diff line change
`@@ -14,6 +14,9 @@ export function merge(...iters) {`
`14`	`14`	`}`
`15`	`15`
`16`	`16`	`export function mergeWith(merger, ...iters) {`
	`17`	`+ if (typeof merger !== 'function') {`
	`18`	`+ throw new TypeError('Invalid merger function: ' + merger);`
	`19`	`+ }`
`17`	`20`	`return mergeIntoKeyedWith(this, iters, merger);`
`18`	`21`	`}`
`19`	`22`